We propose to investigate the contribution of myoglobin toward the economy of red skeletal and cardiac muscle fibers. Specifically, how large is the myoglobin-mediated oxygen uptake of red skeletal and heart muscle cells, and how effectively does it support ATP generation? What are the conditions of oxygen pressure, myoglobin oxygenation and oxygen flux required for optimal mitochondrial function in red muscles? Low concentrations of carbon monoxide may impair myoglobin-facilitated oxygen delivery such that oxygen flux to heart muscle cells may become life-limiting. We will investigate the effect of carbon monoxide on oxygen delivery in isolated cardiac muscle cells directly. We will measure the oxygen uptake of isolated cells from skeletal and cardiac muscle in families of steady states of constant oxygen pressure. The extent of myoglobin oxygenation will be measured spectrophotometrically. In order to overcome limitations of oxygen delivery to separated muscle cells we will add oxygen-binding proteins to the suspending medium. By using a variety of these proteins we will have an internal indicator permitting spectrophotometric determination of oxygen pressure in solution. Oxygen consumption will be followed by simultaneous polarographic measurement of the oxygen-binding protein in the medium. We will abolish the oxygen-binding function of intracellular myoglobin by specific chemical treatment, and determine the quantitative contribution of functional myoglobin toward the oxygen uptake and energy production of red skeletal and cardiac muscle cells.